The present invention relates to aircraft, especially modern transport airplanes, equipped with an electrical flight controls system.
It is known that, in such aircraft in flight, the piloting commands given by the pilot or pilots by means of control members such as, for example, minicontrol columns, are transmitted to computers via position sensors, associated with said control members and generating electrical signals representative of the position of said control members activated by the pilots. Thus, in attitude control, the position of such a control member is converted by said computers into an attitude value and the system controls the movement of the aircraft via elevator aerodynamic control surfaces, so that the actual attitude of the aircraft becomes equal to the value demanded by the pilot, by actuating said control member.
In contrast, on the ground, in the known flight control systems, the deflection commands for the elevator aerodynamic control surfaces (elevator control surfaces) are quite simply proportional to the movements of said control member displaced by the pilot. Hence, if the pilot pulls back fully on said control member, the elevator control surfaces are deflected to their maximum value.
This results in considerable drawbacks.
First of all, on takeoff, there is a risk, if the pilot demands too high an attitude too close to the ground, that the rear part of the fuselage of the airplane will touch the ground and will be damaged.
Moreover, on takeoff, the attitude variation as a function of time--also called rotation rate--varies as a function of the loading of the airplane and of the style of piloting. For a given airplane, this results in a dispersion in the values of the rotation rate, which reduces the "demonstrated performance". In fact, the regulations of the certification authorities define the performance (length of runway, etc.) with margins which depend on the difference between the "maximum rotation rate", the maximum value of the rates of rotation of the longitudinal attitude which are demonstrated on test, and the "mean rotation rate", which is the mean value of these rotation rates. The closer these rates are, the more the potential performance of the airplane is taken advantage of, by reducing the definition margins.